LCDK was first described in 1979 by Cho et al. and the terminology was defined by Slywotzkey et al.. Since then, many studies have documented this unique disease, mostly in the adult population. Only 11 pediatric cases have been documented thus far (Supplementary Table 1)[5–13]. Seven patients were male and four patients were female, with their age ranging from 1.5 months to 16 years. Due to the rarity of the disease, LCDK was not included in the international working group consensus statement for kidney cysts and cystic kidney disease in children.
In our study, LCDK was present in 18 pediatric patients with a mean age of 8 years (range, 3 months to 16 years). Six patients were diagnosed with LCDK less than one year of age. One patient underwent nephrectomy, and 17 patients were conservatively treated by US follow-up. This is the first study to report multiple cases of pediatric LCDK with long-term US follow-up. Lack of awareness of the disease may lead to misdiagnosis and mistreatment, including unnecessary nephrectomy, as in previously reported pediatric cases[5–13]. Of the 11 pediatric reported cases, seven cases underwent surgical excision[5, 6, 8, 10, 12, 13, 15]. Among these seven cases, one patient underwent preoperative chemotherapy before nephrectomy because the radiologist suspected a malignant lesion. Four cases were managed conservatively, and follow-up data were available in two cases. One case showed no interval change after seven years and after one year.
In our study, LCDK was incidentally found in 27.8% patients. Sixty percent of the patients who were incidentally diagnosed with LCDK were under the age of one year. Our cases and previously reported cases that were diagnosed in newborns and during infancy suggest that LCDK may develop during the pediatric period and could be found incidentally during adulthood. The incidental initial diagnosis in adulthood might be possible because LCDK is non-progressive and there is no loss of renal function in the involved patients[2, 3].
The most common modality used in the evaluation of LCDK has been CT, and the disease has characteristic findings: multiple conglomerated simple cysts with normal intervening renal parenchyma[2, 3, 11]. US have also typically been used as the primary imaging tool in previous reports but the role has been underestimated. This might be because most previous studies have been in the adult population. In our study, similar characteristic findings of LCDK were also seen on US. Moreover, seven (38.8%) patients showed multiple hyperechoic foci with ring-down artifacts at intervening normal parenchyma within the cystic lesions on US. Six of seven patients showed focal calcification within the cyst walls on the corresponding CT. One patient developed hyperechoic foci during follow-up; however, the corresponding CT was not available in this patient. This finding is consistent with that of previous studies in the adult population, which demonstrated scattered calcification in cyst walls in 22–42% of the reported LCDK cases on CT[2, 3]. This is a discriminating point from other cystic masses, such as multilocular cystic nephroma, since calcification is rare. The hyperechoic foci observed on US are similar to the previously noted lesions in autosomal recessive polycystic kidney disease (ARPKD). Urine stagnation in dilated tubules, which is a consequence of calcium precipitation, decreases excretion of urinary citrate, and alkaline urine has been suggested to be a possible mechanism for calcification in patients with ARPKD. However, there is a lack of evidence on the pathological correlation to confirm these findings in LCDK, but the appearance and ring-down artifacts suggest the precipitation of some crystalline material, perhaps calcium compounds, in the normal intervening renal parenchyma. Ding et al. pathologically confirmed that cystic septa contain tubules and glomeruli and that the cystic spaces of LCDK were continuous with the dilated collecting ducts in some cases. Lymphocyte infiltrates, foamy histiocyte aggregates, and refractile crystals were occasionally identified in the cystic spaces of LCDK.
LCDK may resemble autosomal dominant polycystic kidney disease (ADPKD), but there are important points of discrimination. LCDK is unilateral and almost always involves only a part of the affected kidney, and coexistence of cystic lesions in other organs such as the liver or pancreas is uncommon[1–3, 11]. ADPKD can affect one kidney before contralateral renal cysts are visualized on imaging studies, mimicking unilateral renal involvement, especially in younger patients. Since the gene for ADPKD has been identified in more than 90% of the patients, genetic evaluation is useful for differential diagnosis[20, 21]. However, in our study, genetic evaluation was not performed in all patients. Two patients showed tiny, simple cysts in the contralateral kidney. There were no cysts in other organs in these patients. Simple cysts in the contralateral kidney have also been reported in the LCDK patients in adult population[2, 3, 22]. In our study, there were six patients who were under one year who had characteristic US findings of LCDK. There may be concerns about the early manifestation of ADPKD in these infant patients. However, only one patient developed a tiny simple cyst in the contralateral kidney during follow-up. Imaging of the family members in the aforementioned patient did not reveal any cysts in the major organs. Renal function was within the normal range during the 56-month follow-up in this patient.
Previously reported LCDK studies have focused on CT and MRI findings because most of the case studies included adult patients. Establishing US findings of LCDK are very important in the pediatric population since US is a radiation- and sedation-free tool that can be easily be used for diagnosis and follow-up examination. From our experience, LCDK is a very stable and benign disease entity, but it requires follow-up imaging to monitor potential interval size changes, as four patients in our study had an interval size increase during follow-up. However, considering the interval growth increase of the normal kidney during pediatric development, the finding was not significant. Establishing US findings of LCDK may help reduce unnecessary additional CT and MRI in pediatric patients. If cystic lesions with typical features of LCDK are noted on US, follow-up US is recommended in the pediatric population.
This study has some limitations. First, the study included a small number of patients and there was only one pathologically proven case. Second, we did not perform genetic studies related to renal cystic disease in all patients. Imaging of family members was performed in only one patient. However, there was no renal insufficiency or cyst in other organs in any patients. Third, since the follow-up duration was relatively long, hyperechoic foci in LCDK might have been more conspicuous due to technological improvement. However, this report describes a noteworthy number of pediatric LCDK cases, and long-term patient follow-up by imaging enhances the clinical significance of this study.